Each neutral (white, grounded conductor) wire should be secured separately under its own lug/set-screw terminal in an electric panel, per National electrical Code (NEC 408.41). Also, a neutral and equipment ground (bare or green) wire cannot share a terminal. If you look carefully at the photo above, you will see that the panel has both defects, which is an indication that a handyman or homeowner has been in the panel adding circuits. Professional electricians know better.

    The reason for the single wire per termination lug requirement is that placing multiple neutrals under one terminal makes it difficult to isolate a circuit for any troubleshooting. The branch circuit breaker is turned off when isolating a circuit, and the neutral is disconnected by removing it from the terminal. If there are two neutrals under the same terminal, the second neutral may also unintentionly be disconnected, even though the circuit is still energized, and this has the potential in some circuits to create an over-voltage condition in the circuit that is still “live.”  Putting a neutral and ground under the same terminal creates a similar issue.

    Although the NEC states that “each grounded conductor shall terminate within the panel board in an indiviual terminal that is not also used for another conductor,” it allows an exception for “grounded conductors of circuits with parallel conductors shall be permitted to terminate in a single terminal if the terminal is identified for connetion of more than one conductor."

   A second exception to the “one wire per terminal” rule is that two—or sometimes three—ground wires can be secured at one terminal, but it is dependent on the manufacturer’s installation instructions and the wire size. This is likely because ground wires are intended for only temporary use and, if a ground wire becomes energized, a breaker should trip shortly afterwards. 

    Also, neutral and ground wires can be terminated along the same termination bus bar in a main service panel (the first panel after the meter), but they must be on separate bus bars in any subpanels, with neutral bus bar isolated (not bonded). 

    For more on this subject, see our blog post When did the code first set a limit of one neutral wire (grounded conductor) connection per lug/set-screw in an electric panel?

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Here’s links to a collection of our other blog posts about ELECTRIC PANELS:

• What causes copper wires to turn green or black in an electric panel?  

• What is the maximum number of circuit breakers allowed in an electric panel?

• When should a corroded or damaged electric panel cabinet or disconnect box be replaced? 

• What is a tandem circuit breaker? 

• When did arc fault circuit interrupter (AFCI) breakers first become required?

• Can an electric panel be located in a closet? 

• Can an electric panel be located in a bathroom? 

• Can you add circuit breakers by different manufacturers to an electric panel if they fit?

• My circuit breaker won't reset. What's wrong?  

• What is a split bus electric panel?

• How do I identify a combination AFCI (CAFCI) circuit breaker? 

• What does a circuit breaker with a yellow or white test button indicate? 

• What is the maximum gap allowed between the front of a recessed electric panel box and the wall surface surrounding it? 

• What are the requirements for NM-cables entering an electric panel box?

• What happens when you press the "TEST" button on a circuit breaker in an electric panel?

• What is a Dual Function Circuit Interrupter (DFCI)? 

• What is the difference between a Combination Arc Fault Circuit Interrupter (CAFCI) and an Arc Fault Circuit Interrupter (AFCI) circuit breaker?  

• What is the difference between "grounded" and "grounding" electrical conductors? 

• What does it mean when a wire is "overstripped" at a circuit breaker?

• Why is an old fuse panel dangerous?  

• Why is the circuit breaker stuck in the middle? 

• What is a double tap at a circuit breaker?

• What is the right electric wire size for a circuit breaker in an electric panel?

• What is the life expectancy of a circuit breaker? 

• My circuit breaker won't reset. What's wrong? 

• Why do some breakers in my electric panel have a "TEST" button on them?

   Visit our ELECTRIC PANELS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.